AbstractRandom copolymers of sarcosine and small amounts of γ‐p‐nitrophenyl‐L‐glutamate (poly(Sar,pNPGlu)) were synthesized and their hydrolyses were investigated in buffer solutions. The reaction courses of their spontaneous hydrolyses consisted of two parts; the initial fast reaction and the subsequent slow reaction. Since the former became shorter as the chain length of copolymer increased, it was attributed to a faster hydrolysis of ester groups near the chain ends.The hydrolysis was considerably accelerated by the introduction of a pyridyl group to a chain end of the copolymer. This was explained by the intrachain catalysis, since the contribution of interchain catalysis was found to be very small. The extent of acceleration was much smaller than in the reaction along the polyacrylamide chain reported by Morawetz et al. The lesser flexibility of polysarcosine chain may account for the difference. Also in the intrachain hydrolysis a large deviation from the first‐order kinetics was observed, which indicated the different reactivities of each ester group positioned at the different separation along the chain from the terminal pyridyl group. Kinetic calculations were carried out using rate constant ki, for the hydrolysis of an ester group attached to the ith residue by the terminal puridyl group. It was found that the dependence of ki on i, Which is the distance between an ester group and the terminal pyridyl group, was more specific than that of intrachain rate constants for the chain effect polymerization of DL‐phenylalanine NCA previously investigated.